Multiplex signaling



DeC 24, i935- H. H. BEVERAGE 2,025,190

MULTIPLEX S IGNALING Filed March 21, 1953 5 sheets-sheet 1 JF f par f2muy .-ff M45/l ,92 A,94 Rf SCH INVENTOR H. H. BEVERAGE BY 'MnM/L/ATTORNEY Dec. 24, '1935. H. H. BEVERAGE 2,025,190

MULTKIPLEX SIGNALING l Filed March 2l, 1933 5 Sheets-Sheet 2 INVENToR H./ERAGE Mu/M/ ATTORNEY H. H. BEVERAGE r2,025,190

MULTIPLEX SIGNALING Y FiledMaroh 21, 1933 5 sheets-sheet 5 Dec. 24,1935.

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Dec. 24, 1935. H. H. BEVERAGE MULTIPLEX SIGNALING Filed March 2l, 1935 5Sheets-Sheet 4 INVENTOR EVEIRAGE C I C: N M 1k I C mx mw N /w-zH/L/ATTORNEY Dec. 24, 1935. H. H. BEVERAGE 2,025,190l MULTIPLEX SIGNALINGvFiled March 2l, 1933 5 Sheets-Sheet 5 lNvENToR H H. Ev RAGE BY /l/OL/ATTORNEY Patented Dec. 24, 193s UNITED STATES PATENT OFFICE RadioCorporation of Delaware of America, a corporation Application March21,1933, semina. 661,947

` 12c1aims. (ci. 17a- 51) This invention relates to a method of andsystem for multiplex signaling. Multiplex systems of various types havebeenknown in the telegraphy and telephony arts, both radio and wired,heretofore. Some of these systems involve the use of a commutator fortime separation of the elements at the transmitter, and ia receiver witha similar commutator for separation of the signal elements at `thereceiver. Systems of this type are in some cases unsatisfactory, due tothe diiiiculty of synchronizing the commutators at the transmitter andat the receiver.

In another type of system the difficulties attending synchronization areovercome by using a commutator for time separation of the signals at thetransmitter and modulation frequency separation at the receiver. Anysystem'which depends upon modulating a carrier withl a multiplicity ofaudio frequencies for obtaining different channels has been found byexperience to be relatively inefficient, since it is necessary to keepthe side band power relatively low as compared with the carrier power.If this is not done, intermodulation or interference between thechannels resuits. A system of this type is sound in theory but inpractice is undesirable, due to the fact that the ratio of noise levelto signal level is extremely high, and due to the relatively -smallamount of power available in the sidebands. In tests made by me it wasfound that the wave modulated with the different frequenciescharacteristic of the signal elements could only be read through aboutve percent as much noise as interrupted continuous wave signals whereall of the transmitter power was available on a single frequency. 4

The most efficient multiplexing systems known heretofore involve the useof continuous wave oscillations at the transmitter with a commutator fortime separation of the continuous wave, and a receiver with a similarcommutator for selecting the signal elements which are received. Thecommutators at the transmitter and at the receiver are driven bysynchronous motors. The motors may be synchronized by a signal impulsesent out from the transmitter. 'Ihis system is again su'bject to thedisadvantage of synchronizing vthe motors at the receiver and thetransmitter.

The primary object of appllcant's invention is to provide a new andnovel method'of and means for multiplexing signals, which method andmeans eliminates all, or substantially all, of the materialdisadvantages noted-v above.

The above -object of applicants invention is accomplishedby a -novelmultiplexing system in which time separation of the oscillations intoelements characteristic of the signal elements is accomplished at thetransmitter by a `commutator. The time separation of the oscillations atthe transmitter is accompanied by 5 changes in frequency of thecontinuous wave. 'I'he resultant transmitted frequencies are Vcharpacteristic of the signal elements. The changes in frequency of thecontinuous Waves which accompany the time separation thereof may beaccomplished in any manner. Preferably, it is accomplished by the use'ofa control current, the intensity of which changes in accordance with thesignal element to be transmitted. `The changes in current intensitycontrol the saturation of a magnetic modulating device, which may beconnected in any desirable manner with any stage in the transmitter toaccomplish frequency shift of the oscillations thereof. l

Any signaling code may be used. Preferably, the Morse cable code isused, and'in using the Morse cable code, dots and dashes are of equallength, but are distinguished in transmission and in reception, that is,after demodulation of the high frequency oscillations has beenaccomplished, by their frequency. For example, the letter A might berepresented by a dot on 1500 cyclesfollowed by a dot on 1000 cycles,while the letter B would be a dot on 1000 cycles followed by three dotson 1500 cycles. In this example, the 1500 cycle dot corresponds to aMorse code dot, while the 1000 cycle dot corresponds to a Morse codedash. No signal corresponds to intervals between elements or betweenwords. Of course, thewpresent invention contemplates the use of threefrequencies, one of which represents a dot, the second of whichrepresents a dash, and

a third which represents spaces or intervals.

In the above example'it is assumed vthat one channel only is being used.The present inven- 40 tion, which relates to multiplexing, contemplatesthe use of 2. 3, or more, channels. Furthermore, each channel may usetwo frequencies and no signal for spacing, or two frequencies formarking andy a third frequency for spacing. In the prior example, fourfrequencies will be necessary v for two channels since no current forintervals and spacing suilices for both channels. If, an interval orspacing frequency is used then live 50 frequencies will be necessary,the additional spacing or interval frequency suiilcing for both erethree channels are used six frequencies, with no,l signal forintervalsand spacing, may vbe used, or seven frequencies where a distinctfrequency is used for spacing and intervals.

Signaling speed is increased by coordinating the commutators for thetime separation of the continuous wave and the automatic keyers vforkeying the transmitter by way of the magnetic modulator so that thespacing intervals on one channel are utilized for marking intervals onother channels and vice versa. This coordination of the time separationcommutator with the automatic keyers increases the speed of keying in amanner analogous to the manner in which the speed of keying is increasedby the invention disclosed in Briggs Patent No. 1,781,361.

The magnetic modulator, the saturation of the core of which is varied bycurrents of different intensity, is of a type to accomplish linearfrequency shift in the continuous waves. 'Ihe transmitter itself is ofthe type in which the carrier is radiated at maximum power at all times,and signaling on the different channels is made Aselective by takinginto account the amount by which the carrier is shifted in frequency bythe various signaling elements.

The time separated frequency shifted signals may be received on acrystal controlled radio frequency receiver. The crystal may be adjustedto match the frequency of the transmitter so that by using heterodynereception the local oscillator beats the received signal to obtain abeat note whichA is zero or substantially zero during intervals orspacing periods when no signals are being transmitted onk eitherchannel.

The heterodyne receiver feeds into a high pass filter circuit which mayinclude the necessary amplifiers. The high pass fllter circuit suppliesthe frequency, if any, to a plurality of lter circuits, there being ailltercircuit foreach differkdrawings in which:

Figure 1 illustrates diagrammatically the manner in which timeseparation of the oscillations is accomplished and the manner in whichcurrents of different intensity are supplied to the magnetic modulator,which may be connected to any suitable transmitter, and shows also therelation of the marking impulses on the individual lchannels and theresultant frequency shift enveloperesulting from the coordination of twochannels;

Figure 2 shows diagrammatically the essential elements of my mutiplexingsystem at the transmitting end; and Figure 2a illustrates in boxl formthe manner in which the transmitters AT #I and AT #2 are controlled by atape in which the -signal characters to be transmitted are punched.

Figure 3 illustrates diagrammatically a receiver of the heterodyne typewhich feeds the beat notes through a high pass lter to the frequencyseparation circuit and from thence to the recorders;

Figure 4 illustrates the characteristics of the.

band pass filters shown schematically in Figure 3;

Figure 5 is the same as Figure 1, except that in Figuresignalingonthreechannelsbytheuse of six frequencies is accomplished; while i Figure 6 issimilar to Figure 2, except that it shows a multiplexing system inwhich'signals may be sent out on three channels. The method ofmultiplexing signals in accordance with my invention vwill be understoodby reference to Figure l of the drawings. The squares designated by thenumerals I and 2 represent commutator segments. 'Ihe shaded 10 squares,which are marked No. I, are all connected together and to a slip ringshown schematically at SR1. In like manner, all of the No. 2 squares, orcommutator segments, are connected together to a second slip ring, shownsche- 15 matically at SR2. A single brush 1 bears on the commutator sothat when the commutator is rotated the brush l makes contact with thesegments I and 2 alternately. The magnetic modulator MM has itssaturating winding 6 connected 20 with the brush 1, with a source ofpotential 9, and by way of a plurality of resistances R1, Rz, R: and R4to a plurality of contacts K1, K2, Ka and K4. Closing of the contactscompletes the circuit `of the l magnetic modulator winding 6 25 throughthe battery by way of one of the -segmentsl or 2 and the slip rings SR1or'SRz. As

. the commutator revolves it connects the transmittcr alternately to thetwo channels by way o! the contacts K1, Ka, K1 and K4. The 'frequency 30of the transmitter T, which is connected by way of the winding I0, withthe magnetic modulator,

,is controlled by the current flowing through the tensities flow throughthe winding 6 of the magnetic modulator. Each slip ring is associated 40with a channel and the current is adjusted to four different values fortwo channels. This is accomplished by .adjusting 'the resistances R1,Rz, R3 and R4 connected with the keys K1, K2, Ks and K4 of the keyingrelays. For purposes of il- 45 lustration, I have assumed that when K1is closed a current I1 will flow in channel 2 and this current willrepresent a dash; current of intensity I-i will flow in channel 2 whenK4 is closed and this will represent a dot; current of intensity I; 50will ilow in channel I when Ka is closed and this will represent a dot;current of intensity Izwill flow in channel I when Kn is closed and thiswill represent a dash; while, current of zero intensity will ilow whenspaces or intervals ap- 55 pear in the signal. 'Ihe keying ,relays maybe separably, biased polar relays, such that a positive line currentoperates one relay while a negative line current operates the other.With no line current the bias will pull both relays to the 60 "off" sideso that no current will flow to the commutator during the idle time onthat channel. These keying` relays may be modified in a number of ways,such as usinga lzero center relay, tube relays,- etc. It is alsopossible toput a fixed 65 current on the modulator and key straight fromthe line with positive and negative impulses. .A preferred form ofrelayhas lbeen shown in Figure 2, which will be discussed in detailhereinafter.

A positive'impulse corresponds to a dot, and a 7o negativev impulsecorresponds to a dash in the Morse cable code. The currents I1, Ia, IJand I4, referred to above as flowing in the circuits when the contactsK1, Ks, Ks and K4 close, reprent the currents flowing in the commutatorsegment corresponding to the characters represented. The little sketchat the bottom of Figure 1 represents the relation between these controlcurrents and the transmitter frequency.` With this in mind it is easy todraw out the combined frequency envelopes of the transmitter, as shown.The frequency envelope of the combined chan nels, that is, channels Iand 2, has been shown in line I. 'I'he envelope of the control currentsent out over channel No. has been shown separately in line 2 and theenvelope of the control current sent out over channel No. 2 has beenshown separately in line 3. These envelopes will be referred to againhereinafter. The manner in which magnetic modulation is accomplished andthe nature of the receiver will be` described first.

Referring to Figure-2, the commutator having the segments I, 2 on itsperiphery may be mounted on a shaft S rotating in a bearing I2.

The shaft S may be driven by a motor |4 at the desired. speed. Sliprings SR1 and SR2 for channels I and 2 may be fastened to a face of thecommutator for rotation therewith.` Brushes B1 and B1 may cooperate withthe slip rings to complete circui/ts by way of magnetic relays MR1 andMRz with automatic keying devices AT1 and ATz. The automatic keyingdevices are driven in synchronism with the commutator by way of bevelledgears I4' and I4" by the motor I4, as shown. 'I'he Wheatstonetransmitters AT1 and ATz may be of the automatic type and are driveninsynchronism at'the same rate of speed through the gears I4' and I4".'I'he connection between the automatic transmitters AT1 and ATZ and lthegearing I4 and I4 respectively on the shaft I5 is such that the spacingintervals of one transmitter coincide with the marking intervals of theother transmitter, and vice versa, that is, the plunger contacts ofautomatic transmitter AT1 for channel I are always up when the plungerson the automatic transmitter ATZ for channel 2 are down, and vice versa.The automatic transmitters AT1 .and ATz are connected by wires I6, |8and 20, 22 respectively with relay windings I1, I9 and 2|, 23respectively of magnetic relays MB1 and MR: respectively. The contactsK3 and K2' are closed under certain conditions by the armaturesassociated with magnetic relay windings |1 and |9 respectively. Thecontacts K1 and K1 are closed under certain conditions by current in thewindings 2| and 23 respectively of magnetic relay MR2. windings I1, |9,2| and 23 are connected by way of resistances R3, R1, R4 and R1respectively to the source of potential 9, which is in turn ,connectedwith the winding 6 of the magnetic modulator MM. 'I'he winding 6 isconnected with the brush 'I bearing on the periphery of the commutator.The automatic transmitters are coordinated to each other so that one ismarking when the other is olf, and vice versa. The operating time lsdivided up equally between each transmitter.v This necessitates the useof signal elements of like time duration. Both transmitters arecoordinated with the commutator so that a segment is under the brush 'lwhen the automatic transmitter AT1 is marking and a segment 2 isunderthe brush 'I when the automatic transmitter AT: is marking. Thus thetime of operation is divided up equally between the two chan# nels. Thecurrent owing in the winding 6 varies the intensity of the ux in thecore of the magnetic modulator. This in turn varies the permeability ofthe iron -core which causes the induc- The armatures of theA tance ofwindlngIll to vary in accordance with the current variations. Thewinding I is shunted across a portion of the inductance 2l, which, incommotion with the condenser 29, determines the frequency o foscillation of vacuum tube 3|. When current flows in winding 6 theinductance of winding I0 decreases. This decreases the total inductancein the oscillating circuit and causes vacuum tube 3| to oscillate at ahigher frequency. 'I'he amount of frequency 10 shift is governed by thevalue of the control current in the winding 6. Choke coils 3l and 39 areinserted in series with control winding to keep radio frequency fromowing in the control circult. A

As an example to further illustrate the operation of this circuit,assume that with no control current flowing in winding 6 of thefrequency shifting device MM the transmitter sends out a frequency of10,000,000 cycles, and that the oscillator associated with the receiverat the other end of the circuit is also adjusted to 10,000,000 cycles,so that the beat note is substantially zero. Now assume that theintensity of the current flowing in resistance R4 is such as to decreasethe in- 25 ductance of MM to such an extent that the transmitterfrequency is increased to 10,000,000 cycles. At the receiver thetransmitter frequency. beats with the local oscillations, which resultsin a beat of 2000 cycles; the resistance R3 permits a cur- 30 rent to owthrough the winding 6, which vdecreases the frequency of theoscillations transmitted suiiiciently to result in a beat note of 1500cycles when the transmitted oscillation beats with the localoscillations at the receiver; the resistance R2 permits sulcient currentto iiow through the winding 6 to lower the transmitted frequency to sucha value that a beat note of 1000 cycles results at the receiver; while,the resistance R1 allows sumc'ient current to flow through the 40winding 6 to produce a beat note at the receiver of 500 cycles. Thus,the letter A" on channel I might be represented by a dot on 1500 cycles(Morse dot) followed by a dot on 1000 cycles (Morse clash); while, theletter B might be represented by a dot on 1000 cycles followed by threedots on 1500 cycles. Of course, where two channels are used the elementsof one letter on one channel should be alternated with elements ofanother letter on the other channel, as illustrated in line I ofFigure 1. The frequency modulated oscillations may be amplified by poweramplifier 25 and radiated or utilized in any desired manner.

While I have described one means for shifting the frequency of thetransmittter, many methods are known to the art, and any of them couldreadily be adapted for use with my invention.

At the receiver, see Figure 3, the signals are picked up on an antennasystem 40 and supplied to a radio frequency amplifier 4i!l followed by ade- 60 tector 44 with associated oscillator 46. The audio frequenciesare amplified in amplifier 48. Oscillations of a frequency substantiallyequal to the frequency of the incoming signal are supplied fromoscillator 46. The oscillator 46 is prefer- 65 ably of the crystalcontrolled type, so that the frequency supplied at the receiver matchesthe frequency of the transmitter and a zero or substantially zero beatnote results when none of the channels are marking. 'Ihis beat note, ifany, 70 may be further amplified in 48 after passing through high passfilter 50. This high pass filter blocks out4 beat notes below a certainfrequency `and passes beat notes between this frequency this high pass.filter is to eliminate harmonics which might be of such frequency as topass through one or more ofthe band pass filters. The beat notesresulting are supplied to the filter circuits 52, 54, 56 and 58 and fromthence-by way of rectiers 60, 62, 64, and 66 to the recorder coils 68and 02;'

At the receiver the transmitter comes in at or near zero beat when bothchannels are oiI. This low frequency beat note is cut off by the highpass :filter 50 so that nothing is heard. As soon as the brush 1 touchessegments No. I on the commutator, the transmitter is keyed to afrequency F3, see line I of Figure 1. A beat note of frequency Fs-Fo, or1500 cycles, in this case, is in the output of the receiver and may beheard. This beat note is passed through the filter 52 and by way of therectier 60 to the coil68 of recorder No. I where it pulls up the pen 14.When the segment No. 2 reaches the brush 1 the beat note instantlychanges to Fi-Fo, or 500 cycles. This pulls down the pen 88 on recorder2. Simultaneously the pen of recorder I has dropped back to zero sincethe frequency F3 has disappeared. When the third segments, that is, thesecond segment No. I, reaches the brush 'I the frequency Fn appearssince contact K2 has been closed by the automatic transmitter AT1. Thisbeat note Fz-Fo, which is equal to 1000 cycles, passes through filter 5Iof channel No. I and pulls down the recording peri of' recorder I tocomplete the letter A on channel I in its original form, as shown inlines I and 2 of Figure l. In this manner the letter B is keyed by theautomatic transmitter AT1 on channel I, while automatic transmitter AT:is completing the letter X and starting on letter Y over channel 2, asshown in Figure 1. The receiver has four band pass filters correspondingto the four frequencies necessary for two channels when no signal onzero-beat is used for spacing.

The characteristicsof the band pass lters which were illustrateddiagrammatically in Figure 3, have been shown in Figure 4. The high passfilter eliminates all beat notes below about 200 cycles and therebyovercomes any diiilculties that might be encountered from harmonics' ofthe spacing frequency. Forexample, if the spacing frequency shouldoverload the audio amplifier, harmonies would be generated which mightpass through the band pass filters and produce false marking on therecorders. By placing the high pass filter 50 (Figure 3) ahead of theaudio amplifier, this dimculty is eliminated.

The four filters are centered at 500, 1000, 1500, and 2000 cycles, andare made as wide as possible in order to allow some drifty between thetransmitter frequency and the local oscillator frequency at thereceiver. The signals may be kept centered in the filters by slight'adjustment of the oscillator at the receiver.` K y.

When it is desired to transmit on three channels the commutator may lbeas illustrated in Figure 5. Heze the segments run in sequence, I to 3and repeated. Three slip rings are necessary and three automatictransmitters of the type similar to the two shown in Figure 2 will benecessary. In view of the fact that the system in which three channelsare used will be clearly understood from the prior description of thesystem, in which two channels have been used, it is thought unnecessaryto describe in detail the system in which multiplexing on three channelsis accomplished. 'I'he system has, however, been illustrated in Figure6.

In Figure 6 parts which correspond to the similar parts in Figure 2 havebeen designated by-like reference symbols.

In Figure 2 the automatic transmitters may be considered as spaced 180degrees apart so that 5 -when one is marking the other is spacing, andvice versa. In the three channel system of Figure 6 the automatictransmitters are spaced by the gearing I4', Il" and I4", 120 degreesapart so that when one is marking the others are 10 spacing. l

In drawing the envelopes of the frequencies sent out by the transmitterover the three channels, in Figure 5, the off signal has been placedintermediate the three signaling frequencies for convenience and tofacilitate understanding of the invention.

In some cases it is desirable to interrupt or cut oi the carrierfrequency oscillations when spacing occurs on. all channels. This may beaccomplishedv as indicated in Figures 2 and 6. When all channels happento be spacing the control current in winding 6 of modulator MM falls tozero because all of the circuits in series with thev modulator areinterrupted. Relay 4I is adjusted 25 so that the minimum current I1,that is, the minimum current which produces a signaling frequency, willhold the relay closed, thereby putting lnormal bias on oscillator grid5I through relay contact 41 from battery I5. As soon as the ccn- 30 trolcurrent drops to zero (when all channels are spacing) relay contact 41is pulled over by a spring S and puts a high negative bias frombatteries 45 and I3 in series on the grid 5I of oscillator 3l. 'Ihisnegative bias interrupts the oscil- 35 lations being generated by saidtube so that no radiation takes place during intervals on all channels.

While the oscillation interrupting means has been shown connected withthe oscillation generator, it will be understood that this interruptingmeans may also be connected with any stage subsequent to the oscillationgenerator. For example, it may be connected with any succeedingamplifier, frequency multiplier, or other relaying stage included in thecircuit between the oscillation generator and the radiating system.

Having thus described my invention and the operation thereof, what Iclaim is:

1. In a multiplex telegraph system, the method of communication by meansof three element signals which comprises generating high frequencyoscillations, producing discrete current impulses of differentintensities characteristic of the signal elements to be transmitted overeach channel, and producing changes in the frequency of the oscillationswhich are determined by the changes in intensity of said currentimpulses, at least two different frequencies being transmitted over eachchannel.

2. 'I'he method of multiplexing signals over a' plurality of channelswhich includes the steps of producing current impulses of constantduration and intensity which are characteristic of signal elements, andproducing high frequency oscillations, the frequencies of which aredetermined by the intensity of said current impulses, there being atleast two different frequencies for each channel, which frequenciesdiffer from the' frequencies use forthe other channels. 7o

3. The method of multiplexing signals over two channels which comprisesproducing two current impulses of like duration but of differentintensities characteristic of the elements of the signal to betransmitted on one of said channels, mOi-75 ducing two other similarcurrent impulses of still other intensities for said other channel, andgenerating oscillations whose frequency is deter- -mined by theintensity of the current impulses.

4. The method of multiplexing signals which includes the steps ofproducing signal impulses of .a predetermined intensity, producingsignal imin the Morse code signaling, and producing oscillations,A thefrequency of which varies substantially in accordance with the intensityof the impulses.

5. The method offmultiplexing signals which includes signaling on aplurality of channels simultaneously by producing current impulses, theintensities of which are characteristic of the sig-l nal elements to betransmitted, there being an impulse of different intensity for eachchannel and for each signal elementen each channel, producingl highfrequency oscillations characteristic of the intensity of each signalimpulse, and 'coordinating said impulses so that the spacing intervalson one channel are utilized for marking intervals on* another channeland vice versa.

6. The combination of an oscillation generator including an electrondischarge device having its electrodes coupled by way of a frequencydetermining lcircuit including, an inductance, and means for keying theloscillations produced by varying the'value of' said inductance, of awinding coupled to said inductance, a'second winding magneticallyrelated to said flrstnamed Winding,4

a commutator, a plurality of groups of segments on said commutator, abrush bearing on said commutator segments, said brush being connected-.to one terminal of said last named winding. slip rings on saidcommutator, there being a slip ring a resistance connecting each of saidcontacts by way of a common source of potential tothe other terminal ofsaid last named winding, magnetic relays associated with said contacts,and automatic keying means in circuit with the magnetic relays, therebeing a keying means for each group of segments, and a motor for drivingsaid commutator and said keying means in synchronism. 7. l Multiplexreceiving meansc'omprising, a re.

' ceiver responsive to a band of frequencies, heterodyne demodulatingmeans coupledto said re-v ceiver, a -high passfllr coupled to Asaiddemodui. v

lating means, a plurality of pairs of band pass filters connected withsaid high pass lter, and a single recording means connected to eachpair4 of band pass filters. y

8. Signaling means comprising an-electron dis- 5 charge device havinganode, cathode, and control grid electrodes, a reactance couplingsaidanode, cathode and control grid for producing sustained oscillations andfor determining the frequency of the same, electrical means forcontrolling the ef- 10 fe'ctive value of said reactance for varying thefrequency of the oscillations produced over a -predetermined range, andmeans in circuit with said electrical means for applying'a potential tosaid control grid electrode to render said device 16 inoperative. y A

9. The method of multiplexing which includes thev steps of producingoscillations, interrupting said oscillations to produce impulsesof highfrequency oscillatory energy, and simultaneously 20 .changing thefrequency of the` time separated the steps of coordinating said channelsso that marking intervals on one channel utilize the spacing intervalson another channel, and interrupting said oscillations when spacingintervals appear simultaneously on al1`channels.

1l. A device for multiplexing signals comprising a transmitter,l amodulator connected therewith, a plurality of sources of impulses ofdifferent intensity, there being employed a plurality of impulses ofdifferent intensity for each channel, and automatic means responsive tosignal characters for selectively `associating said sources i with saidmodulator.

12. A ,multiplex telegraph receiver for receiving a plurality offrequencies each of which is characteristic of a signal impulse elementto be transmitted which 'comprises an energy collector, heterodynedemodulating means coupled to s aid collector, a filter coupled to theoutput of said'45 demodulating means, and a plurality of additional'nlters in circuit with said rst filter, each of said plurality of ltersbeing individual to oneof the Asignal impulse elements to be received,at least two filters being provided for each channel and a translatingdevice for each channel which is responsive to the signal impulsesreceived over the filters in said channel.

HAROLD H. BEVERAGE. se

